Gravity's subtle influence in the quantum world has been directly observed for the first time.

On tiny scales, nature makes particles behave according to curiously rigid rules. For instance, negatively charged electrons trapped around a positive nucleus under the pull of the electromagnetic force cannot have any energy they want -they have to fall into a set of distinct energy levels.

In the same way, the pull of gravity should make particles fall into discrete energy levels. But because gravity is extremely weak on small scales, the effect has been impossible to spot. "To be able to measure it, you need to suppress interference from all the other fields," says Valery Nesvizhevsky of the Laue-Langevin Institute in Grenoble, France.

Now Nesvizhevsky and his colleagues have achieved the feat using a beam of neutrons. Neutrons were ideal because they're neutral, so they don't feel the electromagnetic force and can ignore its quantum rules.

Experts say it is a convincing result from an extremely tricky experiment. "The difficulty of this measurement should not be underestimated," says Thomas Bowles of Los Alamos National Laboratory in New Mexico. "In the quantum realm, the gravitational force is so weak that it is difficult to observe quantum effects."

Bouncing neutrons

Nesvizhevsky's team took a beam of ultracold neutrons with tiny energies, moving from left to right at less than eight metres per second. Under the force of gravity, the neutrons fell down onto a reflecting mirror and bounced off it before arriving at a detector.

The team could limit the energies of the neutrons arriving at the detector by placing an absorbing material at different heights above the mirror. The material mopped up all the neutrons that bounced too high.

Forgetting quantum mechanics, you would expect neutrons with any energy to arrive at the detector. But no neutrons appeared unless the neutron-mop was at least 15 micrometres above the mirror. This means the neutrons have to have a certain, minimum energy (equal to 1.41 x 10-12 electronvolts) in the Earth's gravitational field.

Step up

There were also hints that neutron transmission took little leaps at different, higher energies, corresponding to higher quantum levels. However, the team has still to confirm this.

Nesvizhevsky says the technology is exciting because it could test some other key ideas in physics - for instance, whether or not the neutron carries some minuscule amount of electric charge. "If it's there, it's very, very small," says Nesvizhevsky.

It could also put on trial the equivalence principle, a famous concept of Einstein's. It says that all particles, regardless of their mass or composition, should fall with the same acceleration in a uniform gravitational field.

Journal reference: Nature (vol 415, p 297)

19:00 16 January 02

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I have a hypothesis about gravity. It could falsefied by showing that electrons have gravitational attraction for one another. Showing protons some gravitational attraction would not do it, as they have quarks with so opposite electric charge.

I suppose it could be confirmed by seeing if the strength of the gravitational constant falls within parameters suggested by the hypothesis. Here goes...

Gravity is a by-product of subatomic particles reacting to electromagnetic waves that pass through their "location".

There is a net difference in the "pull" force produced by an EM wave that has the opposite charge as the particle verses the "push" force produced by an EM wave that has the same charge. This is because during the minute time period that the EM wave of the charge is passing through the "location", the subatomic particle reacts to the event.

Consider; if a wave of the same charge passed through the particle, it would alter its "location" so as to move in the opposite direction of the wave. This motion would weaken its force of "impact" during the time of the event (wave passing through). I suppose this is like the Doppler effect on wave energy.

Now consider the opposite situation. A wave from an opposite charge moves through the particle "location". During the tiny life of the event the particle will be attracted to the source, so the relative motion will draw the particle into the incoming wave. This will strengthen the its force of attraction during the time the wave is passing through.

The force known as "Gravity" is therefore the net difference between the opposite verses the same charge of wave passing through a particle "location". The attractive EM force gets stronger as it passes through, the repulsive force gets weaker. This tiny difference explains why gravity is so tiny relative to the EM force, and why no anti-gravity has ever been found.

I am sure you get stuff like this all the time. If it is nonsense just saying so if fine. I won't be offended if you do not have time to explain why. Ahban

What? You've never read "Transgressing the Boundaries" by Paul Sokol? He proves, rather convincingly, that gravity is a social construct and an artifact of human existence. The quantum theory proves it. (I could give you the exact link so that you could check it out, but I'm too blasted lazy to walk a few feet to my library and pull out my copy of "Fashionable Nonsense").

I have a hypothesis about gravity. It could falsefied by showing that electrons have gravitational attraction for one another.

Well, I didn't follow the argument, but it's simple to show that electrons have gravitational attraction. Electrons make up one part in 1800 or so of the mass of hydrogen, say, which is more than 2.5 times the fraction of the mass of uranium made up by electrons. All you would have to do is measure the ratio of inertial masses of a mass of hydrogen and a mass of uranium (you could do this with a torsion balance), and compare it to the ratio of their gravitational masses (you'd do this with a beam balance). The ratios would be measurably different. Archimedes might have used water and lead; the ratio of electron mass fraction would have been a bit smaller than 2.5, but he wouldn't have missed the effect.

But it does not necessarily follow that they also have a maximum energy in the Earth's gravitational field.

Nor would there be a maximum energy.

Thus, isn't the precise hypothesis ("the pull of gravity should make particles fall into discrete energy levels") still unproven?

The lowest energy levels, just like the energy levels of an electron in an atom, are the most widely spaced. As the particle assumes a higher and higher energy level, the spacing between the energy levels becomes ever smaller and less easily distinguished, until ultimately it becomes a continuum band. That is to say, there is an energy above which any amount of energy is permitted. But for slow enough neutrons, only certain energies are permitted.

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